Introduction:
An SN1 reaction completes the hydrolysis of 2-chloro-2-methyl propane via a two step, nucleophilic substitution reaction. The rate of the reaction is dependent on both of the reagents, these are the nucleophile and the electrophile. The solvent can also influence the reaction rate. Depending if the solvent is polar protic or aprotic the transition state and the stability of the intermediate carbocation will differ. When using a polar protic solvent, the reaction rate of the SN1mechanism is sped up due to the solvent stabilizing the intermediate carbocation. This stabilizing effect, on the intermediate carbocation, decreases the overall energy needed to complete the reaction. In this experiment we will also explore how the reaction rate is effected as the percentage of water is increased and the percent of solvent is decreased throughout four trials. Since water is more polar than either the isopropanol or acetone, we expect that the reaction rate will increase as the ratio of water increases for both solvents.
This is a well-written paragraph: information-rich and concise! Note that the situation with acetone/water mixtures is additionally complicated by the fact that as the % water increases, you increase the protic-ness of the solvent while actually decreasing the overall polarity. Whoa! weird, huh?
Procedure: This lab procedure was carried out per the instructions of the handout received from Dr. Higginbotham, titled "CH242/338 Organic Chemistry II Laboratory Nucleophilic Substitution Reactions".
Data
Reaction time in seconds for the solvents: Acetone and Isopropanol, Our group used isopropanol (Trial 1) which data was taken by your group? I don't see that you specify anywhere.
Table 1
Acetone Trial 1
Acetone Trial 2
Isopropanol Trial 1
Isopropanol Trial 2
Flask #1(Positive control
2
0
1
1
Flask #2
358
315
400
486
Flask #3
98
75
209
81
Flask #4
33
23
42
16
Flask #5
11
13
19
8
This data is set out very nicely in this table. Good job.
Table 2
Material
Flask #1 (Positive control)
Flask #2
Flask #3
Flask #4
Flask #5
% H2O
52%
50%
60%
70%
80%
[NaOH]
Miniscule amnt
--------------------
--------------------
--------------------
--------------------
[HCl]
Miniscule amnt
--------------------
--------------------
--------------------
--------------------
[RCl]
None
50%
40%
30%
20%
The [RCl] does not change, does it? You put 2.0 mL into each of your test tubes, and the total volume in those reactions was always 10 mL.
Conclusion and Analysis
The intentions of this experiment were to investigate what effect the solvent has on an SN1 reaction. The two solvents used were Acetone and Isopropanol. Given the characteristics of SN1 reactions, the greater the polarity of the solvent the faster the reaction will occur. Isopropanol is more polar than acetone. This is actually UNtrue! Acetone has a much larger dipole moment than isopropanol. There the Isopropanol reaction should have gone faster. Do you mean "When comparing isopropanol mixtures to similar acetone mixtures?" In addition to examining SN1 reaction rate using two different solvents increased water percentage was factored into the experiment. Water is more polar than both the solvents used again, not true and greatly contributed to the quickened reaction speed as its percentage was increased in both solvents. However this conclusion cannot be assumed given the experimental data. The isopropanol trial 1 reaction speed was slower than either of the Acetone trials.Trial 1 was a positive control, with HCl added in immediately so that you could see two things: 1) the color change, and 2) any lag time between the formation of acid and the stopping of your stopwatch. These results are not in agreement with the overall understanding of the increased reaction speed of SN1 when a polar protic solvent is used. Possible reasons for discrepancies in the data comparison of the two solvents are possible errors made during the lab procedure. These could include:
A dirty test tube, flask or stir bar, that may have contaminated the mixture and altered the reaction time. As one group experienced during one of the trials a dirty flask artificllly increased the rate of the reaction. Once the flask was properly cleaned and the trial repeated, the data matched the trend.
Improper measurement of either the water or solvent could have caused an error in the data. But! You can not report "improper measurement" to your boss (that would be me) and expect them to forgive you for this error. Avoidable errors should not be listed in the error analysis in your report.
When looking at the percent composition of water to solvent (Table 2) the trend of the experimental data supports the original hypothesis that increased ratio of water to solvent increases the reaction rate.
Post Lab Questions:
Suggest a different chiral alkyl halide that might be used if we want to get evidence from polarimetry that our reaction actually proceeds by SN1 rather than SN2. Potassium hydroxide
I would like an explanation for this answer. Why did you choose this?
Name three other solvents that might be effective at completing the SN1 reaction that we performed. Methanol, ethanol and formamide. Dimethyl formamide? "Formamide" by itself is not the name of anything.
This report earned the following scores for: format (2/2) style (2/2) data (2.5/3) quality of result (1/1) quality of reported data (1/1) conclusion (0.5/2) error (0.5/1) post-lab questions (0.5/2) for a total of 10/14. Parts of your report are very good, other parts have significant problems. Perhaps some more group editing would help--have everyone in the group look over everyone else's contributions.
Introduction:
An SN1 reaction completes the hydrolysis of 2-chloro-2-methyl propane via a two step, nucleophilic substitution reaction. The rate of the reaction is dependent on both of the reagents, these are the nucleophile and the electrophile. The solvent can also influence the reaction rate. Depending if the solvent is polar protic or aprotic the transition state and the stability of the intermediate carbocation will differ. When using a polar protic solvent, the reaction rate of the SN1mechanism is sped up due to the solvent stabilizing the intermediate carbocation. This stabilizing effect, on the intermediate carbocation, decreases the overall energy needed to complete the reaction. In this experiment we will also explore how the reaction rate is effected as the percentage of water is increased and the percent of solvent is decreased throughout four trials. Since water is more polar than either the isopropanol or acetone, we expect that the reaction rate will increase as the ratio of water increases for both solvents.
This is a well-written paragraph: information-rich and concise! Note that the situation with acetone/water mixtures is additionally complicated by the fact that as the % water increases, you increase the protic-ness of the solvent while actually decreasing the overall polarity. Whoa! weird, huh?
Procedure: This lab procedure was carried out per the instructions of the handout received from Dr. Higginbotham, titled "CH242/338 Organic Chemistry II Laboratory Nucleophilic Substitution Reactions".
Data
Reaction time in seconds for the solvents: Acetone and Isopropanol, Our group used isopropanol (Trial 1)
which data was taken by your group? I don't see that you specify anywhere.
Table 1
Table 2
Conclusion and Analysis
The intentions of this experiment were to investigate what effect the solvent has on an SN1 reaction. The two solvents used were Acetone and Isopropanol. Given the characteristics of SN1 reactions, the greater the polarity of the solvent the faster the reaction will occur. Isopropanol is more polar than acetone. This is actually UNtrue! Acetone has a much larger dipole moment than isopropanol. There the Isopropanol reaction should have gone faster. Do you mean "When comparing isopropanol mixtures to similar acetone mixtures?" In addition to examining SN1 reaction rate using two different solvents increased water percentage was factored into the experiment. Water is more polar than both the solvents used again, not true and greatly contributed to the quickened reaction speed as its percentage was increased in both solvents. However this conclusion cannot be assumed given the experimental data. The isopropanol trial 1 reaction speed was slower than either of the Acetone trials.Trial 1 was a positive control, with HCl added in immediately so that you could see two things: 1) the color change, and 2) any lag time between the formation of acid and the stopping of your stopwatch. These results are not in agreement with the overall understanding of the increased reaction speed of SN1 when a polar protic solvent is used. Possible reasons for discrepancies in the data comparison of the two solvents are possible errors made during the lab procedure. These could include:
A dirty test tube, flask or stir bar, that may have contaminated the mixture and altered the reaction time. As one group experienced during one of the trials a dirty flask artificllly increased the rate of the reaction. Once the flask was properly cleaned and the trial repeated, the data matched the trend.
Improper measurement of either the water or solvent could have caused an error in the data. But! You can not report "improper measurement" to your boss (that would be me) and expect them to forgive you for this error. Avoidable errors should not be listed in the error analysis in your report.
When looking at the percent composition of water to solvent (Table 2) the trend of the experimental data supports the original hypothesis that increased ratio of water to solvent increases the reaction rate.
Post Lab Questions:
Suggest a different chiral alkyl halide that might be used if we want to get evidence from polarimetry that our reaction actually proceeds by SN1 rather than SN2. Potassium hydroxide
I would like an explanation for this answer. Why did you choose this?
Name three other solvents that might be effective at completing the SN1 reaction that we performed. Methanol, ethanol and formamide. Dimethyl formamide? "Formamide" by itself is not the name of anything.
This report earned the following scores for: format (2/2) style (2/2) data (2.5/3) quality of result (1/1) quality of reported data (1/1) conclusion (0.5/2) error (0.5/1) post-lab questions (0.5/2) for a total of 10/14. Parts of your report are very good, other parts have significant problems. Perhaps some more group editing would help--have everyone in the group look over everyone else's contributions.